1. Field of the Invention
The present invention relates generally to a method for measuring the viscosity of paint. More particularly, the present invention relates to a system and method for measuring the viscosity of a layer of wet paint after it has been applied to a surface.
2. Description of Related Art
The measurement and control of paint viscosity is an important part of any paint application process. Viscosity measurements are especially important in spray painting systems where small variations in paint viscosity can drastically affect the quality, durability and appearance of the paint coating.
Typically, the viscosity of paint is monitored while the paint is still in a spray tank and prior to applying the paint to a surface. A standard liquid viscometer is utilized for this type of paint viscosity monitoring. The results of the paint viscosity monitoring are used to determine the propensity of the paint to run, sag, or peel.
The problem with measuring paint viscosity prior to application is that the actual viscosity of the paint layer on the painted surface is usually different from the viscosity measured in the spray tank. Accordingly, measurement of paint viscosity in the spray tank only provides an indirect indication of the actual viscosity of the paint at the application site. Changes in parameters which may occur during the operation of the painting system can result in the surface viscosity of the applied paint changing while the viscosity of the paint in the spray tank remains the same. Unfortunately, such variations are only noticed when the applied paint layer runs, sags or otherwise becomes unacceptable.
The most desirable method for measuring and monitoring paint viscosity would be to measure the viscosity of the paint after it has been applied to a surface. Direct viscosity measurement of the layer of paint after application is more meaningful because it provides a direct indication of the likelihood of the paint to run, sag or peel. Further, direct measurements of the viscosity of the applied layer of paint can be made at selected times after application to provide direct information on paint curing behavior. There are also numerous other advantages which are inherent in being able to directly measure the viscosity of paint once it is applied to a surface. As in any measurement or monitoring system, direct measurement of a parameter, such as viscosity, is preferable to indirect measurement.
Although there are numerous advantages inherent in measuring the viscosity of paint at the application site, a major problem involves being able to make such direct measurements without destroying or otherwise permanently disturbing the paint layer. Destruction or disturbance of the paint layer is especially undesirable for automobiles, airplanes, appliances, and the like, where a flawless finish is important.
As is apparent from the above, it would be desirable to provide a system and method for directly monitoring the viscosity of a layer of wet paint on a surface during the painting process. Further, the process must be non-destructive in that the disturbance or destruction of the paint is minimized. Such a non-destructive and direct testing method would enable one to more accurately control paint viscosity to avoid the running, sagging, and peeling of paint which may result when viscosity is measured only in the spray tank.